We　investigate　the　quantum　phase　transitions　(QPTs)　of　a　four-level　system　in　a　noisy　environment.　The　system　is　composed　of　a　four-level　atom　which　is　driven　by　classical　fields　and　simultaneously　coupled　with　a　quantum　field　mode.　A　second-order　dissipative　phase　transition　(DPT)　is　observed　by　combining　unitary　processes　with　dissipation　dynamics.　The　analytical　expression　for　the　DPT　in　the　anisotropic　Rabi　model　is　given.　We　demonstrate　that　the　QPT　in　an　open　four-level　system　is　characterized　as　several　boundaries,　which　is　completely　different　from　that　in　a　closed　system.　In　addition,　our　model　is　robust　against　strong　atomic　spontaneous　emission,　providing　a　promising　platform　for　observing　DPT　in　an　open　system　and　studying　the　related　dynamics　associated　with　DPT.　©　2019　American　Physical　Society.